1. Field of the Invention
The present invention concerns a method for vapor deposition of a substrate with a layer of a needle-shaped x-ray luminophore with at least one alkali metal as well as the x-ray luminophore itself. As used herein x-ray luminophore scintillator with fluorescence as well as storage luminophore with emission by stimulation with laser light. Fluorescence is generally understood as the excitation of a luminophore with high-energy radiation (UV, x-ray) to cause emission of low-energy radiation (emission). In a storage luminophore, higher-energetic emission (for example 420 nm) is triggered with low-energetic radiation (for example 680 nm) since the “residual energy” in the x-ray has been “stored”.
2. Description of the Prior Art
X-ray luminophores are generally used in medical technology and destruction-free material testing. In these applications, scintillators with spontaneous emission under x-ray excitation are used, as well as storage luminophores with formation and storage of electrons and holes with subsequent photo-stimulated emission (PSL) upon irradiation with, for example, red light are used. The x-ray luminophores based on an alkali halide thereby assume a very particular role. Examples are CsI:Na in an x-ray intensifier, CsI:Tl in a-Si detectors or, of late, CsBr:Eu as a storage luminophore plate as described in Proc. of SPIE Vol. 4320 (2001), “New Needle-crystalline CR Detector” by Paul J. R. Leblans et al., pages 59 through 67.
In all cited medical applications of alkali halogenide it is common that a high x-ray absorption must ensue to achieve a high DQE in the alkali halide layer, and the signal (light) must be clear over the noise. A high x-ray absorption is achieved by an approximately 500–600 μm thick alkali halogenide layer. The problem of a still-too-low light yield is still present in all cited medical applications. In particular the low light yield of the storage luminophore represents a problem that is still not completely solved.
In U.S. Pat. No. 5,028,509, example 14 describes the use of CsBr:Eu as a storage luminophore, produced from CsBr and Eu2O3. The general formula for the combination of the alkali halide luminophore (Cs and Br) is specified as follows:(M1−x.MIx)X.aMIIX′2.bMIIIX″3:dB,whereby M=Cs or Rb, MI is at least one alkali metal from the group Li, Na, K, Rb and Cs, MII is at least one bivalent metal from the group Be, Mg, Ca, Sr, Ba, Zn, Cd, Cu and Ni, MIII is at least one metal from the group Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ga and In, B is an activator that is at least one metal from the group Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Gd, Lu, Sm, Y, TI, Na, Ag, Cu, Mg, Pb, Bi, Mn and In, X, X′ and X″ are the same or different and represent a halogen atom from the group F, Cl, Br and I.
Known from PCT Application WO 01/03156 A1 is a production method for a stimulatable storage luminophore of the general formula CsX:Eu for the combination of the luminophore for the Cs-bromide and/or -chloride. Such a storage luminophore was produced from CsBr and EuBr2, EuBr3 or EuOBr.
European Application 1 113 458 describes a method is described for coating a substrate in which Eu is introduced as EuX2, EuX3, and EuOX.
A common feature of all of these luminophores is that the doping material is a relatively simple molecule. These simple molecules are often attached on interstitials.
In tests with storage luminophore powders, it has been shown that microscopically small phases of the doping material can be formed in the alkali halide. In vacuum-deposited layers of CsBr:Eu, these phases have not been found before. This is due to the Eu concentration in the layer being only maximally 3000 ppm (0.3 mol %), conditional upon production (different vapor pressures of CsBr and EuBr2), while given the use of powder phases an optimal PSL signal was present only given Eu concentrations >1 mol %.